The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2001-381672 filed on Dec. 14, 2001, which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a recording apparatus, a recording method therefor and a program therefor, and particularly relates to a recording apparatus for printing a multi-gradation image by forming three or more kinds of dots different in density per unit area by means of area coverage modulation, density modulation, or mixture of those gradations; a recording method for the recording apparatus; and a program for the recording apparatus.
2. Description of the Related Art
A color ink jet printer having inks of a plurality of colors has been proposed as one of digital color image output apparatuses. The color ink jet printer has been used broadly for printing images. In the ink jet printer, ink particles ejected from a plurality of nozzles integrally arrayed in a head are landed on a printing medium such as a sheet of paper while the head is moved in a direction (main-scanning direction, first scan direction) perpendicular to a direction (sub-scanning direction, slow scan direction) in which the printing medium is fed. Thus, ink dots ate formed to record an image. Black (K), cyan (C), magenta (M) and yellow (Y) are used as the basic colors of the inks.
In such an ink jet printer, in order to improve the printing speed, bi-directional printing is performed in which ink is ejected in both the forward direction and the reverse direction of the head while the head is moved in the main-scanning direction. In the case of the bi-directional printing, the inks of K, C, M and Y are landed on the printing medium in that order in the forward direction. On the contrary, the inks of Y, M, C and K are landed on the printing medium in that order in the reverse direction.
Due to the difference in color order in which the inks are landed, there is a problem that there is a slight variation in hue for the following reason. That is, when blue (B) is formed out of the inks of C and M, there is a slight difference in hue between B formed out of C and M in that color order in the forward direction and B formed out of M and C in that color order in the reverse direction. As a result, there occurs a problem that B different in hue like stripes in the sub-scanning direction is printed though B uniform in hue should be printed essentially. This phenomenon refers to color shift caused by the difference in color order in which the inks are landed. In a one-path bidirectional printing, width of the stripe is as long as length of the nozzle line so that the color shift becomes distinctly visible. This is a big problem. Incidentally, the one-path bidirectional printing performs recording in one path in the main scanning direction with respect to a region having the same length as the nozzle line and transfers a recording paper by the length of the nozzle. Subsequently, the one-path bidirectional printing repeats to perform recording in one path in an opposite direction to the previous path with respect to another area having the same length as the nozzle line.
The principle that the hue changes due to the difference in the color order in which the inks are landed will be described using the case where B is formed out of C and M. In a printing medium into which the inks easily infiltrate, the C ink landed first stays in the surface and inside of the recording medium, and the M ink landed next comes around to the lower side of the C ink and permeates the recording medium. Thus, the hue becomes rich in C landed first. That is, in the printing medium into which the inks easily infiltrate, the color of the ink landed first becomes dominant.
On the other hand, in a printing medium into which the inks hardly infiltrate, the C ink landed first stays in the surface of the medium, and the M ink landed next stays on the C ink or flows to a portion where the C ink is not put. Thus, the hue becomes rich in M landed later. That is, in the printing medium into which the inks hardly infiltrate, the color of the ink landed later becomes dominant.
There have been proposed several methods for avoiding such a change in hue, in JP-A-Hei.6-106736 in which a plurality of recording pixels are allocated to every pixel of data, and in JP-A-Hei.11-314382 in which a color conversion table is changed.
In addition, in JP-A-Hei.6-106736, one pixel of mixed color is expressed by a plurality of pixels of simple colors (for example, one pixel of red is expressed by two pixels of magenta and yellow not overlapping each other). Therefore, there is such a problem that the dimensions of image data are doubled lengthwise and widthwise or the density is made half However, there are further problems in the recording methods in the related art as follows. That is, the recording methods require information about the scanning direction of the head. In addition, different processes have to be applied to a recording area at the time of outward scanning of the head and a recording area at the time of homeward scanning of the head, respectively so that the color in the former recording area is in agreement with the color in the latter recording area.
Also, in JP-A-Hei.6-106736, a mixed color in a single pixel is represented by a plurality of pixels each having single color (for example, red in a single pixel is represented by two pixels which have magenta and yellow, respectively, without overlapped each other). Therefore, the size of image data becomes twice in lengthwise and breadthwise directions and/or density is reduced to half. These are also problems.
It is an object of the invention to provide a recording apparatus in which, when forming a color image on a recording medium while repeating reciprocating motion of a head, it is not necessary to take the scanning direction of the head into consideration for quantizing image data and to change the size of an image, and it is possible to prevent the reduction of the density and to reduce color shift caused by the difference of the order in which dots of a plurality of colors are landed, so that the image quality can be improved; a recording method for the recording apparatus; and a program for the recording apparatus.
In order to solve the foregoing problems, according to a first aspect of the invention, there is provided a recording apparatus including a recording head, an input section, and a quantization section. The recording head can form a plurality of kinds of dots, which are different from each other in density, per unit area for every single color by means of at least one of area coverage modulation and density modulation. The recording head ejects a plurality of colors. The input section inputs image data having a gradation value for every pixel. The quantization section quantizes the inputted image data so that number of pixels in which the kind of dot for at least one color is different from the kinds or dots for the other colors in one and the same pixel is higher than number of pixels on which dots having the same kind are superimposed and macroscopic hue is equal to a case in which dots having the same kind are superimposed in all pixels. The recording head is reciprocated to record on a recording medium based on a quantization result obtained by the quantization section.
According to the first aspect, the input section inputs image data having a gradation value for every pixel. The is quantization section quantizes the image data inputted by the input section. At this time, the quantization section quantizes the inputted image data so that number of pixels in which the kind of dot for at least one color is different from the kinds of dots for the other colors in one and the same pixel is higher than number of pixels on which dots having the same kind are superimposed and macroscopic hue is equal to a case in which dots having the same kind are superimposed in all pixels. In other words, the quantization is carried out so as to suppress the number of pixels in which dots having the same density are superimposed or dots having the same size are superimposed. Then, A recording medium is recorded based on the result of the quantization by the quantization section while the recording head repeatedly reciprocate, which can form a plurality of kinds of dots, which are different from each other in density, per unit area for every single color by means of at least one of area coverage modulation and density modulation. Incidentally, the macroscopic hue refers to the hue of the following single color When an ensemble of a large number of minute pixels including a plurality of colors are looked from a normal visual distance by naked eye, the ensemble is recognized a single color due to the integration effect of naked eye.
With this construction, it is prevented to superimpose the dots for different colors having the same kind on one and the same pixel. When kinds (density or area such as dot size) of dots for a plurality of colors, which form one pixel, are different, color forming a dot having large area or high density has a strong influence. For example, cyan has a strong influence in a pixel formed of a large droplet of cyan and a small droplet of magenta. Also, magenta has a strong influence in a pixel formed of a small droplet of cyan and a large droplet of magenta. These facts don""t depend on color order in which the droplets are landed on a recording medium. Therefore, the color shift caused by difference in color order in which dots are landed between a time when the head scans in a forward direction and a time when the head scans in a reverse direction can be reduced.
Also, the quantization is carried out so that macroscopic hue is equal to a case in which dots having the same kind are superimposed in all pixels. Therefore, it is not necessary to change the size of an image and reduction in density also can be suppressed.
According to a second aspect of the invention, the quantization section quantizes the inputted image data so that the number of pixels in which the kind of dot for at least one color is different from the kinds of dots for the other colors in one and the same pixel is higher than number of pixels in which dots each having higher density than a predetermined density are superimposed.
According to a third aspect of the invention, the quantization section quantizes the inputted image data so that the pixels in which the kind of dot for at least one color is different from the kinds of dots for the other colors in one and the same pixel is not arrange in a deviation manner.
According to a fourth aspect of the invention, the quantization section quantizes the inputted image data so that the pixels in which the kind of dot for at least one color is different from the kinds of dots for the other colors in one and the same pixel are arranged two-dimensionally without deviation while number of dots for each color in the pixels and number of dots for each kind in the pixels are not changed.
According to a fifth aspect of the invention, the quantization section carries out second quantization by redetermining a kind of dot for each color with reference to a first quantization result.
According to a sixth aspect of the invention, in the second quantization, a kind of dot for each color is redetermined based on a dot redetermination ratio, which is prepared in advance, so that the macroscopic hue is equal to the case in which dots having the same kind are superimposed in all pixels.
A recording method according to the invention can be applied to the recording apparatus according to the first to sixth aspects of the invention. Similarly, a program according to the invention also can be applied to the recording apparatus according to the first to sixth aspects of the invention.